Question

define phase of SHM ​

Answer 1

Phase of a point in SHM is the angle made by the point, in uniform circular motion whose projection is that simple harmonic motion, with the initial point of motion at the centre of the circular motion or the mean position of thesimple harmonic motion.

Answer 2

Phase is one variable which can be related to all other variables easily (position, velocity, and acceleration). That would mean knowing the constants of SHM and the phase would be enough to completely define any SHM. In adding two or more simple harmonic motions, phase would be a very important term.